Circuit breaker



July 26, 1966 Filed July 25, 1962 R. L. WHITE CIRCUIT BREAKER 5 Sheets-Sheet 2 'U'A/T 7260/7 5254/65@ Vroem/5% July 26,

R. L. WHITE CIRCUIT BREAKER Filed July 2:5, 1962 3 Sheets-Sheet 5 fx S INVENTOR.

United States Patent .C

3,263,128 CIRCUIT BREAKER Richard L. White, 432 W. Sierra Madre Ave., Glendora, Calif.

Filed July 23, 1962, Ser. No. 211,790 19 Claims. (Cl. 317-33) The present invention relates to automatic electrical controls, and it relates more particularly to a solid-state direct-current circuit breaker.

The usual prior art circuit breaker includes, for example, athermal element, or an electromagnet and mov- 'able armature. In the latter type of instrument, the electromagnet trips the armature when the circuit breaker is actuated, to open associated contacts, so as to interrupt the current flow to the associated electrical circuit. As is Well known, the prior art circuit breaker can be'constructed to respond to over-load conditions, to under-load conditions, or to other malfunctions in the controlled circuit and in its supply source.

An object of the present invention is to provide an improved circu-it breaker of the direct-current solid-state type which is extremely fast acting; and which operates on the order, for example, of 1,000 times the speed of the usual movable armature prior-.art type of circuit breaker. The improved circuit breaker of the invention is capable, for example, of responding within 6 microseconds after the sensing of the corresponding abnormal condition by the instrument.

Another object of the -invention is to provide such an improved circuit breaker of the solid-state type which does not require any moving parts in its operation.

Yet another object of the invention is to provide such an improved direct-current solid-state circuit breaker which is extremely Ireliable in its operation.

A further object of the invention is to provide such an improved direct-current solid-state circuit breaker which is small in size, Iand which is relatively simple and inexpensive in its construction.

A still further object is to provide such an i-mproved direct-current solidstate circuit breaker which exhibits a low voltage drop during its normal closed, or conductive, operating condition.

According to one embodiment of the present invention, a circuit breaker comprises a pair of controlled rectifiers coupled to a sensing element so that in the on condition, one controlled rectifier conducts and the other one does not. When the current or voltage exceeds a certain limit, the sensing element, which can be a tunnel diode or a Zener diode, turns on the non-conducting controlled rectiier, which in turn makes the gate of the initially conducting controlled rectifier go negative, thereby turning it oit and opening vthe circuit. The circuit remains in the off condition until reset.

The improved circuit breaker of the invention, because of its extremely high response speed, is particularly suited for use in conjunction with computers, data processors and the like, to protect the apparatus `and prevent the burning out of expensive components thereof.

Voltage and current transients in the above-mentioned systems and apparatuscan cause damage, or destroy components, before the usual prior art thermal or magnetic circuit breakers can operate. The improved circuit breaker of the invention can give protection to the equipment, even under transient conditions, because of its extremely fast response characteristic.

Although the improved circuit breaker of the invention is particularly useful in conjunction with computers, data processors, and the like, as mentioned above, it will be evident as the description proceeds that the circuit breaker of the invention has general utility.

The features of the invention which are believed to be new are set forth in the claims. The invention itself, however, may best be understood by reference to the followingdescription, when taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a circuit diagram of a solid state circuit breaker constructed in accordance with the concepts of a first embodiment of the invention, and which responds to a current over-load condition to operate and open the load circuit associated therewith;

FIGURES 2 and 3 are characteristic curves of dilerent -components utilized in the circuit of FIGURE l;

FIGURE 4 is a circuit diagram of a circuit breaker incorporating the concepts of the invention and similar to the system of FIGURE 1, but which is constructed to be actuated in response to an excessive voltage condition across the associated load;

. `FIGURE 5 is a characteristic curve of a 'Zener diode component which is used in the circuit of FIGURE 4;

FIGURES 6 and 7 are solid-state circuit-breaker systems vincorporating the concepts of a second embodiment of the invention, these latter systems being consructed to respond to a current overload condition in the associated load;

FIGURE 8 is a circuit diagram of a circuit breaker constructed to incorporate the concepts of the second embodiment of the invention, and which responds to an excessive voltage condition across the associated load; and

FIGURE 9 is a circuit diagram of a dilicerent embodiment which responds. to an excessive voltage condition across the associated load.

The solid-state current-responsive circuit breaker system of FIGURE 1 includes a 'pair of input terminals 10 and 12 which are connected across the positive terminals of any usual source of direct-current line voltage. The terminal 12 is connected, for example, to the positive side of the line, and this terminal is connected to the anode of a silicon controlled rectifier 14.

The cathode of the silicon controlled rectifier 14 is connected to an output terminal 16, and the gate electrode of the silicon controlled .rectifier 14 is connected to the anode of a second silicon controlled rectifier 20. The gate electrode of the second silicon controlled rectifier 20 is connected to an output terminal 22. The load 24 is connected across the output terminals 16 and 22.

The cathode of the silicon controlled lrectifier 20 is connected to the terminal 10 which, in turn, is connected to the negative side of the line. The cathode of the silicon 'controlled rectifier 20 is also connected to the cathode of a tunnel diode 26. The anode of the tunnel diode 26 is connected to the junction of the gate electrode of the silicon controlled rectifier 20 and the output electrode 22.

The silicon controlled rectifier has been recently developed, and a full description of this device may be found, for example, in a publication entitled Controlled Rectifier Manual, published by the Rectifier Component Department of the General Electric Company, at Auburn, New York.

The characteristic curve of a typical silicon controlled rectifier is illustrated in FIGURE 2 in which the current (I) is plotted against voltage (V). It will be observed that in the reverse direction, the silicon controlled rectifier exhibits a normal Zener characteristic. In the forward direction, the device exhibits a voltage breakdown which is a function of the positive gate current. The voltage Ibreakdown for different gate currents (181, Igz, 1K3) being illustrated.

The silicon controlled rectifier may be operated on direct current, and it may .be rendered non-conductive by using a negative gate current. The turn-on gain of the device is very high, so lthat a few milliamperes of gate cur- 3 rent will render the device conductive, so as to enable a relatively high current load to be passed through the device. However, the turn-off gain of the device is low, so that an appreciable portion of the load current must be shunted ofi through the gate electrode for the controlled rectifier to regain its current blocking condition.

The tunnel diode is a recently developed device, and a description of the tunnel diode may be found, for example, in United States Patent 3,033,714, which issued May 8, 1962. The characteristic of the tunnel diode is shown in FIGURE 3, in which current (I) is plotted against voltage (V). The characteristics of the tunnel diode are very useful in developing a gate signal for the silicon controlled rectifiers in the circuit of FIGURE 1, when a threshold level of current through the load 24 is exceeded. The tunnel diode has 'a very stable peak current at which it switches from a low resistance, low voltage drop, to a relatively high resistance, high voltage drop. This characteristic of the tunnel diode, combined with its extremely low voltage drop during normal operation, makes the tunnel diode an ideal sensing element in -the circuit of FIGURE 1.

In the circuit of FIGURE l, the controlled rectifier 14 is normally conductive, and this rectifier carries the normal load current owing through the load 24. This current also iiows through the .tunnel diode 26, and the tunnel diode remains in its low resistance/low voltage drop state, so long as the normal current flows through the load 24.

Un-der the above-described conditions of normal current iiow through the load 24, the circuit breaker may be considered to be in its normal closed condition. Under this condition, both the silicon controlled rectifier 14 and the tunnel diode 26 exhibit a low voltage drop, so that almost the entire line voltage is introduced across the load 24, as is desire-d, and the extraneous losses in the circuit are reduced to a minimum.

Should the load current through the load 24 exceed a predetermined threshold, indicating, for example, a short circuit in the load, the tunnel diode 26 immediately switches from its low resistance, low voltage state to its high resistance, high voltage state. The sudden change in voltage across the tunnel diode 26 is applied to the gate electrode of the silicon controlled rectifier 20, which is normally non-conductive. The resulting current through its gate electrode in response to the above-mentioned increase in voltage, however, causes the controlled rectifier to fire. The result-ing conductivity of the controlled rectifier 20 shunts a portion of the load current through the gate electrode of the controlled rectifier 14. This is a negative current, and it is of sufiicient amplitude to trip the circuit breaker, so as to cause the controlled rectifier 14 to become non-conductive and open the circuit to the load 24. The controlled rectifier 20 stops conducting when the controlled rectifier 14 becomes nonconductive. This action is extremely rapid, and the controlled rectifier 14 is rendered non-conductive in a time interval of the order, for example, of several microseconds following the overload condition in the load 24.

The circuit breaker of FIGURE 4 is similar in some respects to the circuit of FIGURE 1, and like elements have been indicated by the same numerals. In the circuit of FIGURE 4, however, the tunnel diode 26 has been replaced by a Zener diode 30. The cathode and anode of the Zener diode are connected from the cathode of the controlled rectifier 14 to the gate electrode of the controlled rectifier 20, respectively. Zener diodes are well known to the art at present, and a ltypical characteristic curve for the Zener diode is shown in FIGURE 5, in which the voltage (-V) is plotted against the current (4).

The circuit of FIGURE 4 responds to a voltage increase across t-he load 24 above a predetermined threshold. This voltage increase causes Ithe Zener diode 30 to break down, which allows current to pass to the gate electrode 4. of the controlled rectifier 20. This current causes the controlled rectifier 20 to become conductive, so that it turns ofi the controlled rectifier 14 in the manner described above in conjunction with the system of FIGURE 1.

Therefore, when the voltage across the load 24 rises to a level exceeding the `breakdown voltage of the Zener diode 30, t-he resulting potential applied to the gate electrode of the normally non-conductive controlled rectifier 20 causes the controlled rectifier 20 to conduct. The conduction of the controlled rectifier 20, in the manner described above, causes a current iiow through the gate electrode of the controlled rectifier 14 which is sufficient to render the latter controlled rectifier non-conductive. This action occurs almost instantaneously, and it serves to break the supply of current to the load 24.

A solid-state circuit breaker system embody-ing a secf ond embodiment `of the invention is illustrated in FIG- URE 6. The system of FIGURE 6 responds .to an increase in current through the load 24 to interrupt the supply of power to the load.

The system of FIGURE 6 includes a pair of input terminals and 52 connected respectively to the positive and negat-ive terminals of the source of direct-current line voltage. The terminal 50 is connected to the anode of a silicon controlled rectifier 54, and the terminal 52 is connected to an output terminal 56,

The cathode of the controlled rectifier 54 is connected to the collector of an NPN transistor 58. The transistor 5S may be of the type presently designated 2N696. The emitter of the transistor 58 is connected to the gate electrode of a second silic'on controlled rectifier 60 and to the anode of a tunnel d-iode 62. The controlled rectifiers 54 and 60 may Ibe similar to the controlled rectifiers described above, and may each be of the type presently designated 2N1597. The cathode of the controlled rectifier 6i) is connected to an output terminal 64, as is the cathode of the tunnel diode 62. The load 24 is connected between the output terminals S6 and 64. The tunnel diode 62 may be similar to the tunnel diode discussed above, and it may be the type presently designated 2N2933.

The Vanode of the controlled rectifier 60 is connected to the gate electrode of the controlled rectifier 54. A diode `66 has its anode connected to the gate electrode of the silicon controlled rectifier 54, and its cathode connected to the base of the transistor 58.

During normal operation of the circuit of FIGURE 6, the controlled rectifier 54, the transistor 58, and the tunnel diode 62 are all conductive. This enables the current iiow from the direct-current line voltage to fiow through the load 24. Also, because of the relatively low voltage drops across the elements S4, 58, and 62, there are relatively low losses in the circuit. During this normal condition, the NPN transistor 58 is held conductive by the current flow through the gate of the controlled rectifier S4 and through the diode 66. The controlled rectifier 60, as in the previous embodiments, is non-conductive during normal operation of the circuit. Also, as in the previous embodiments, and as mentioned above, the tunnel diode 62 is in its low voltage, low lresistance state during normal operation -of the system.

Should the current through the load 24 increase beyond a predetermined threshold, as established by the peak current of the tunnel diode 62; which increase may, for example, be due to an undesired increase in the supply voltage .or to a short circuit in the load 24, the following operation occurs:

The tunnel diode 62 switches to its high voltage, high resistance state, and the resulting voltage across the tunnel diode switches the controlled rectifier 60 to its conductive state. The resulting conductivity of the controlled rectifier 60 draws reverse current from the gate of the controlled rectifier 54, making the gate go negative, and removing the bias from the transistor 58, which, in turn, serves to increase the voltage drop across the transistor.

rllhe increase in voltage drop across the transistor 58 causes lmore current to fiow through the silicon controlled rectifier 60, and the action is cumulative until the controlled rectifier 54 is rendered fully non-conductive. When the controlled rectifier 54 is fully non-conductive, all current through the load 24 is interrupted.

The above-described action is almost instantaneous, in the same manner as was the case with the previous emn bodiments. Therefore, any malfunctions in the load 24,

or any excessive variations in the direct-current'line voltage, causes the circuit of FIGURE 6 to terminate almost immediately the flow of current through the load 24. The controlled rectifier 54 is held in its state of non-conductivity until the circuit is reset. Y

The circuit of FIGURE 7-is similar to the circuit of FIGURE 6, and similar elements have been designated by the same numbers. The circuit of FIGURE 6 represents the basic circuit, and the circuit of FIGURE 7 represents a practical circuit incorporating the concepts of the basic circuit. The circuit of FIGURE 7 includes an on-o switch 70 which has a movable arm connected to the cathode of the tunnel diode 62, to the cathode of the controlled rectifier 60, and to the anode of diode 71. The switch '70 also has an on fixed contact connected to the load 24 and to the negative terminal of capacitor 72, and an off fixed contact connected to the terminal 50. The positive termin-al of capacitor 72 is connected to the anode Iof the diode 74 and to the cathode of diode 71. The cathode of diode 74 is connected to the electronic reset terminal 75, to the gate of the controlled rectifier 54, and to resistor 77, the other end of which is connected to the anodes of the diode 66 and the controlled rectifier `60. The capacitor 72 may have a capacity, for example, of .O5 microfarad. The resistor 77 may, for example, have a resistance of 150 ohms.

The circuit of FIGURE 7 operates in much the same manner as the circuit of FIGURE 6, as described above. A potential applied to the terminal 75 will reset the controlled rectifier 54 electronically. If preferred, switch 70 can be used to manually reset the controlled rectifier 54. When switch 70 is in the off condition, capacitor 72 charges through diode 71. In the .on condition, capacitor 72 discharges through the gate ofthe controlled rectifier 54 and the base of the transistor 58, resetting the circuit breaker. When capacitor 72 is discharged, it is effectively removed from the circuit because of the diode 74.

The system of FIGURE 8 is similar to that of FIG URE 6, except that the system of FIGURE 8 responds to excessive voltage increases across the load 24 to trip and thereby interrupt the fiow of current through the load. In the circuit of FIGURE 8, components similar -to those of FIGURE 6 have been designated by the same numerals.

The tunnel diode 62 is replaced by a Zener diode 80 in FIGURE 8, as the sensing element, The emitter of the transistor 58 is connected directly to the output terminal 64 and to the cathode of the Zener diode 80. The anode of the Zener diode 80 is connected to the gate electrode of the controlled rectifier 60, the cathode of which is connected to input terminal 52.

When the voltage across the load 24 exceedsthe breakdown voltage of the Zener diode 80, the Zener di-ode causes a voltage to be applied to the gate of the controlled rectifier 60. This renders the controlled rectifier 60 conductive, and the system operates in the manner described in conjunction with FIGURE 6 to discontinue the application of power to the load `24.

The circuit of FIGURE 9 is similar to the circuit of FIGURE 8, and similar elements have been designated by the same numbers. The circuit of FIGURE 8 represents one basic circuit for a voltage circuit breaker, and the circuit of FIGURE 9 represents a modified basic circuitfor a voltage circuit breaker, in which a tunnel diode 81 is used in place of the Zener diode 80. The tunnel diode 81 is connected in series with resistor 83 and the combination is in parallel with the load 24. The gate of the controlled rectifier `60 is connected to the junction between tunneled diode 81 and resistor 83. One end of the resistor 85 is connected to the gate of the controlled rectifier 54 and to the electronic reset terminal 86. The other end of the resistor 85 is connected to the anodes of diode 66 and controlled rectifier 60.

The circuit of FIGURE 9 operates in much the same manner as the circuits of FIGURES 6 and 8, as already described.

For special cases, sensing elements such as resistors, thenmistors, and incandescent lamps could be used instead of a tunnel diode or a Zener diode. If` a time delay were desired, a capacitor could be connected in parallel across the sensing element.

The invention, as described, provides an improved solidstate protective circuit of the circuit breaker type. `The improved circuit and system of the invention does not require movable parts, and it includes solidstate elements to provide the desired control and. current interruption functions.

The improved system of the invention is most advantageous in thatV it is relatively simple in its concept; and yet it is capable of extremely reliable operation, and of operating almost instantaneously to interrupt the current to the protected equipment upon the happening of any Imalfunction in the equipment, or in the associated circuits.

While particular embodiments of the invention have been shown and described, modifications may be made, and it is intended in the claims to cover such modifications as fall within the scope of the invention.

What is claimed is:

1. A circuit for interrupting the electrical current from a current source through a loa-d in response to a voltage across the load in excess of a predetermined threshold, said circuit including:y

` (a) a first controlled rectifier including an anode, a

cathode and a gate electrode,

(fb) first circuit means for connecting said anode and cathode of said first controlled rectifier in series with one terminal of said source and a first terminal of said load,

(c) a second con-trolled rectifier including an anode, a

cathode and a gate electrode,

( d) second circuit means for connecting the anode and cathode of said second controlled rectifier in series with said gate electrode of said first controlled recti- Ifier and with the other termin-al of sa-id source, and

(e) a Zener diode connected to said first terminal of said load and to said gate electrode of said second controlled rectifier and responsive to the volt-age across said load in excess of said predetermined threshold for controlling the conduction of said second controlled rectifier.

2. A circuit for interrupting the electrical current from a direct current source through a load in response to a voltage across the load in excess of a predetermined threshold, said circuit including:

(a) a first normally conductive controlled rectifier including an anode, a cathode and a gate electrode,

(Ib) first circuit means for connecting said an-ode and cathode of said first controlled rectifier in series with one ter-min'al o-f said source and a first terminal of said load,

(c) a second normally non-conductive controlled rectifier including an anode, a cathode and a gate e1ectrode,

(d) second circuit means for connecting the anode and cathode of lsaid second controlled rectifier in serie-s with said gate electrode of said fir-st controlled rectifier and the other terminal otf said source, and

(e) a Zener diode connected to said first terminal of said load and to said gate electrode of said second controlled rectifier and responsive to a voltage across said load in excess of said predetermined threshold to apply a breakdown voltage to said second controlled rectifier to render said second control-led rectifier conductive, so as to cause said second con trolled rectifier to render said first controlled rectifier non-conductive.

3. A circuit .for interrupting the electrical current from a current source through a load in response to a control effect from the load, said circuit including:

(a) a first controlled rectifier including an anode, a

cathode and a gate electrode,

(vb) `an electronic discharge device including an input e-lectrode, an output electrode and a control electrode,

(c) first circuit means for connecting said anode and cathode of said first controlled rectifier and said input and output electrodes of said electronic discharge device in series with said source and said load,

(d) a second controlled rectifier including an anode, a

cathode and a gate electrode,

(e) second circuit means for connecting the anode and cathode of said second controlled rectifier in series iwith said gate electrode of said firs-t controlled rectifier,

(f) a Zener diode connected to said load and to said gate electrode of said second controlled rectifier and responsive to said control effect from said load for con-trolling the conduction of said second controlled rectifier, and

(g) circuit means for coupling the anode of said second controlled .rectifier to the contr-ol electrode of said electronic discharge device.

4. A circuit for interrupting the electrical current from a direct current source through a load in response to a voltage across the load in excess of a predetermined threshold, said circuit including:

(-a) Ia first normally conductive controlled rectier including an anode, a cathode and a gate electrode,

(b) .a transistor having a base electrode, a collector electrode and an emitter electrode,

(c) first circ-uit means for connecting said anode and cathode of said first controlled rectier and said collector and emitter of said transistor in series with one terminal of said source and a first terminal of said load, the second terminal o'f said load being connected to the other terminal of said source,

(d) a second normally non-conductive controlled rectifier including an anode, a cathode and a gate electrode,

(e) a second circuit means for connecting the anode and cathode of said second controlled rectifier in series with said gate electrode of said first controlled rectifier and the other terminal of said source,

(t) a Zener diode connected to said first terminal of said load and said gate electrode of said second controlled rectifier for introducing a breakdown volt- -age to said second controlled rectifier when the voltage across said load exceeds said predetermined threshold to cause said second controlled rectifier to become conductive and thereby tend to render said first controlled rectifier non-conductive, and

(g) a diode connected to the anode of said second control-led rectifier and to the base of said transistor to render said transistor non-conductive when said second controlled rectifier is rendered conductive.

5. A circuit for interrupting the electrical current from a direct-current source through a load in response to an overload condition, comprising:

a pair of input terminals adapted to -be connected to said source;

a pair of output terminals adapted to be connected to said load;

rst and second translating means, each having a first element, a second element, and a control element;

a sensing element responsive to an overload condition;

means coupling said input terminals, said first and second elements of said first translating means, said sensing element, and said output terminals in a series circuit;

means coupling said control element and said second element of said second translating means across said sensing element; and

means coupling said control element of said first translating means with the first element of said second translating means.

6. The circuit of claim 5 wherein each of said first yand second translating means are controlled rectifiers.

7. The circuit of claim 6 wherein said sensing element is a tunnel diode.

8. A circuit for interrupting the electrical current from a direct-current source through a load in response to an overload condition, comprising:

a first controlled rectifier including an anode, a cathode and a gate electrode;

a sensing element responsive to an overload condition;

means coupling said s-ource, the anode and cathode of said first controlled rectifier, said sensing element and said load in a series circuit;

a second controlled rectifier including an anode, a

cathode and a gate electrode;

means coupling said gate electrode and said cathode of said second controlled rectifier across said sensing element whereby said second controlled rectifier will be caused to conduct When said sensing element senses an overload condition; and

means coupling said gate electrode of said first controlled rectifier to said anode of said second controlled rectifier whereby conduction of said second controlled rectifier will render said first controlled rectifier non-conductive.

9. The circuit of claim 8 wherein said sensing element is a tunnel diode.

10. A circuit for interrupting the electrical current from a direct-current source through a load in response to an overload condition, comprising:

a pair of input terminals adapted to be connected to said source;

a pai-r of output terminals adapted to be connected to said load;

first and second translating means, each having a first element, a second element, and a control element;

a sensing element responsive to an overload condition;

a third translating means having an input electrode, an

output electrode, yand a control electrode;

means coupling said input terminals, said first and second elements of said first transl-ating means, said input and output electrodes of said third translating means, said sensing element and said output terminals in a series circuit;

means coupling said control element and said second element of said second translating means across said sensing element; means coupling said control element of said second translating means with the first element of said second translating means; and 4 means coupling said control electrode of said third translating means with said first element of said second translating means.

11. The circuit of claim 10 wherein each of said first and second translating means are controlled rectifiers and said third translating means is a transistor.

12. The circuit of claim 11 wherein said sensing element is a tunnel diode.

13. A circuit for interrupting the electrical current from a direct-current source through a load in response to an overload condition, comprising:

a first controlled rectifier including an anode, a cathode land a gate electrode;

a tunnel diode;

a transistor having an emitter, a collector and a base;

means coupling said source, the anode and cathode of said first controlled rectifier, the emitter and collector of said transistor, said tunnel diode, and said load in a series circuit;

a second controlled rectifier having an anode, a cathode and a gate electrode;

means coupling said gate electrode and said cathode of said second controlled rectifier across said tunnel diode whereby said second controlled rectifier will be caused to conduct when the voltage acnoss said t-unnel diode rises as a result of an overload condition;

means coupling said gate electrode of said first controlled rectifier to said anode of said second controlled rectifier whereby conducti-on of said second controlled rectifier will render said first controlled rectifier non-conductive; and

means coupling the base of said transistor to the anode of said second controlled rectifier.

14. The circ-uit of claim 13 wherein said means coupling said base includes a diode.

15. The circuit of claim 14 further comprising: switching means coupled in said series circuit between said tunnel diode and said load, said switching means being operable to complete or break said circuit;

vresistance means are coupled between said gate electrode of said first controlled rectifier and the coupling of said base and said anode of said second controlled rectifier;

second and third diodes;

me-ans coupling said diodes between said gate electrode of said controlled rectifier and the cathode of said second controlled rectifier; and

capacitor means coupled between the junction of said second and third diodes and the side of said load coupled to said tunnel diode by said switching means.

16. A circuit for interrupting the electrical current from a direct-current source through a load in response to an overload condition, comprising:

a pair of input terminals adapted to be connected to said source;

a pair of output terminals 4adapted to tbe connected to said load;

first and second translating means, each lhaving a first element, a second element, and a control element;

=a sensing element responsive to an overload condition;

resistance means;

means coupling said input terminals, said first and second elements of said first translating means, said resistance means and said sensing element in a series circuit;

means coupling said output terminals across said resistance means and said sensing element;

and second translating means are controlled rectifiers.

18. The circuit of claim 17 wherein said sensing element is a tunnel diode.

19. A circuit for interrupting the electrical current from a direct-current source through a load in response to an overload condition, comp-rising:

a first controlled rectifier including an anode, a cathode and a gate electrode;

a tunnel diode;

a .transistor having an emitter, a collector and a base;

yresistance means;

means coupling said source, the anode and cathode of said first controlled rectifier, the emitter and collector of said transistor, said resistance means and said tunnel diode in .a series circuit;

means coupling said load -across said resistance means and said tunnel diode;

a second controlled rectifier having an anode, a cathode and a gate electrode;

means coupling said gate electrode and said cathode of said second controlled rectifier across said tunnel diode whereby said second controlled rectifier will be caused to conduct when the voltage across said tunnel diode rises as .a resultof an overload condition;

means coupling said gate electrode of said first controlled rectifier to said anode of said second con- References Cited by the Examiner UNITED STATES PATENTS 6/1962 Gutzwiller 307-885 2/1964 Kauders 3l7-33 X OTHER REFERENCES Blake: Static Relays (text), Engineering Publishers,

1961 (page 173).

50 STEPHEN W. CAPELLI, Primary Examiner.

ARTHUR GAUSS, Examiner.

D. D. FORRER, Assistant Examiner. 

5. A CIRCUIT FOR INTERRUPTING THE ELECTRICAL CURRENT FROM A DIRECT-CURRENT SOURCE THROUGH A LOAD IN RESPONSE TO AN OVERLOAD CONDITION, COMPRISING: A PAIR OF INPUT TERMINALS ADAPTED TO BE CONNECTED TO SAID SOURCE; A PAIR OF OUTPUT TERMINALS ADAPTED TO BE CONNECTED TO SAID LOAD; FIRST AND SECOND TRANSLATING MEANS, EACH HAVING A FIRST ELEMENT, A SECOND ELEMENT, AND A CONTROL ELEMENT; A SENSING ELEMENT RESPONSIVE TO AN OVERLOAD CONDITION; MEANS COUPLING SAID INPUT TERMINALS, SAID FIRST AND SECOND ELEMENTS OF SAID FIRST TRANSLATING MEANS, SAID SENSING ELEMENT, AND SAID OUTPUT TERMINALS IN A SERIES CIRCUIT; MEANS COUPLING SAID CONTROL ELEMENT AND SAID SECOND ELEMENT OF SAID SECOND TRANSLATING MEANS ACROSS SAID SENSING ELEMENT; AND MEANS COUPLING SAID CONTROL ELEMENT OF SAID FIRST TRANSLATING MEANS WITH THE FIRST ELEMENT OF SAID SECOND TRANSLATING MEANS. 